This invention relates to a method for the removal of scale from band steel by virtue of electrolysis.
Generally band steel is produced by first hot rolling a strip of steel to approximate dimensions and subsequently cold rolling it to exact dimensions of the finished product desired. The hot rolling treatment results in the surface of the band steel being covered with scale. To ensure the dimensional accuracy of the finished product, therefore, it is prerequisite that preparatory to the cold rolling treatment, the band steel should be stripped completely of the scale.
For the purpose of such scale removal, there has heretofore been employed the practice of pickling by use of sulfuric acid or hydrochloric acid. This practice, however, has proved disadvantageous since the safe disposal of the spent acid from pickling is costly and the spent acid, if improperly disposed of, causes environmental pollution. Under the circumstances, development of a method for the removal of scale from band steel by virtue of electrolysis has been earnestly desired.
Heretofore, there has been suggested a method for the removal of scale from band steel by virtue of electrolysis (Japanese Pat. No. 313,084). This method aims to remove scale from the surface of stainless steel by subjecting the scale-covered stainless steel to an electrolytic reaction in the electrolyte of a salt solution of pH 7.0-1.0, and thereafter giving to the stainless steel a chemical aftertreatment in a dilute acid having a concentration of less than 30% at a temperature of not more than 80.degree. C. Since the scale on the surface of stainless steel has a thickness of about 0.1.mu., it can easily be removed by this method. In the case of the scale formed on the surface of band steel, however, since it has a thickness of about 10.mu., it cannot be easily removed by this method.
By the electrolytic method described above, removal of scale from band steel can be attained to some extent by lengthening the duration of electrolysis. One possible measures for providing such a lengthened duration of electrolysis would be to greatly increase the dimensions of the electrolytic cell used and another would be to slow the speed of the motion of band steel through the electrolytic cell. Commercially, however, these measures prove infeasible.
An object of this invention is to provide a method for effective and economic removal of the scale of band steel by virtue of electrolysis. By the term "band steel" used herein is meant a hot rolled steel plate manufactured from a carbon steel having a carbon content of not more than 0.15% and a manganese content of not more than 0.6%.